Issue 14, 2023

Effect of strand molecular length on mechanochemical transduction in elastomers probed with uniform force sensors

Abstract

The mechanical properties of a polymer network reflect the collective behavior of all of the constituent strands within the network. These strands comprise a distribution of states, and a central question is how the deformation and tension experienced by a strand is influenced by strand length. Here, we address this question through the use of mechanophore force probes with discrete molecular weights. Probe strands, each bearing a mechanochromic spiropyran (SP), were prepared through an iterative synthetic strategy, providing uniform PDMS-functionalized SP force probes with molecular weights of 578, 1170, and 2356 g mol−1. The probes were each doped (9 mM) into the same silicone elastomer matrix. Upon stretching, the materials change color, consistent with the expected conversion of SP to merocyanine (MC). The critical strain at which measurable mechanochromism is observed is correlated with the strain hardening of the matrix, but it is independent of the molecular length of the probe strand. When a network with activated strands is relaxed, the color dissipates, and the rate of decoloration varies as a function of the relaxing strain ([small epsilon, Greek, macron]r); faster decoloration occurs at lower [small epsilon, Greek, macron]r. The dependence of decoloration rate on [small epsilon, Greek, macron]r is taken to reflect the effect of residual tension in the once-activated strands on the reversion reaction of MC to SP, and the effect of that residual tension is indistinguishable across the three molecular lengths examined. The combination of discrete strand synthesis and mechanochromism provides a foundation to further test and develop molecular-based theories of elasticity and fracture in polymer networks.

Graphical abstract: Effect of strand molecular length on mechanochemical transduction in elastomers probed with uniform force sensors

Supplementary files

Article information

Article type
Paper
Submitted
19 Jan 2023
Accepted
13 Mar 2023
First published
15 Mar 2023

Polym. Chem., 2023,14, 1646-1655

Effect of strand molecular length on mechanochemical transduction in elastomers probed with uniform force sensors

T. Ouchi, W. Wang, B. E. Silverstein, J. A. Johnson and S. L. Craig, Polym. Chem., 2023, 14, 1646 DOI: 10.1039/D3PY00065F

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